The invention relates to a method for cleaning liquid cooling lubricants, especially those with a mineral-oil base, which preferably are in continuous circulation in metal-processing facilities, in which a deposition filtration system is provided.
Above all, liquid oil-based or emulsion-based cooling lubricants are used in metal-cutting facilities which cut off chips to cool and to lubricate cutting locations and to carry off abraded particles formed as a result. The liquid cooling lubricant is in continuous circulation, and to supply several metal-processing machines, the liquid cooling lubricant is re-introduced through a central supply facility into the individual machines.
To achieve ideal cross-sectional images of the workpiece, it is necessary to clean the liquid cooling lubricant after use. For this reason, continuously operating cleaning facilities are included in the circuit in which facilities the used cooling lubricant is freed, above all, from solid abraded metal particles by means of sedimentation facilities, magnets, or filters.
Deposition filters, in which a suspension is formed from the cooling lubricant together with a filtering aid and thereafter filtered through a carrier web with deposition of the filtering aid, are used especially for the extra-fine purification of the mineral-oil-based cooling lubricant.
Such a process is known from DE 25 37 384. In this process, highly surface-active, adsorbing, solid substances are used as filtering aids. Activated earth which has an average particle size of less than 0.06 mm is particularly preferred.
Systems are also known as deposition filters which work by deposition of internally-produced contamination. However, these processes do not offer a sufficient cleaning under high performance requirements. Under normal circumstances, therefore, filtering aids are deposited in a separate circuit before the actual filtration occurs by means of the interconnected second circuit. The contaminated oil or contaminated emulsion, which has been contaminated by grits and grinds, metal filings, or other types of contamination such as rolling scale or draw-in scale, travels from the metal-cutting machines or machine tools through a dirt return line into a dirty liquid buffer container. From there, the dirty liquid is conveyed via filter pumps through cartridge filters, in the process of which the contamination accumulates on the cartridges and forms a filter cake of dirt.. The oil purified by means of the filter cartridges travels into a clean tank and is once again transported from there to the machines or to sites of use.
One disadvantage of the known methods is that large quantities of the filtering aids are necessary. Disposal of these filtering aids is extremely difficult because this involves toxic substances which have to be disposed of following special disposal techniques. In addition, the filtration intervals are of relatively short duration since the filtering aid layer very quickly becomes loaded with the absorbed contamination, so only small amounts of liquid can be filtered.